Luminescent and absorptive metal-coated emulsions for micro-velocimetry

• We synthesize silver-coated oil droplets that are both luminescent and absorptive
• Droplets are first coated with a polydopamine layer onto which a silver layer is deposited by a redox process.
• The metal-coated particles have a mean diameter of 6 µm and their density has been matched to the density of water.
• We use these particles as tracers to measure the velocity profile in a microchannel with a rectangular cross-section.
• We confirm the predictions of the Stokes equation with results comparable to those of common polystyrene particles.

Fluorescent latex beads have been widely used as tracers in microfluidics for the last decades. They have the advantages to be density matched with water and to be easily localizable using fluorescence microscopy. We have recently synthesized silver-coated oil droplets that are both luminescent and absorptive, by first coating the oil interface with a polydopamine layer and then depositing a silver layer by a redox process. They have a mean diameter of 6 μm and their density has been matched to the density of water by adjusting the thickness of the metallic layer. In this work we used these particles as tracers to measure the velocity profile of an aqueous solution in a PDMS microchannel with a rectangular cross-section. This allowed us to confirm the predictions of the Stokes equation with results comparable to those of common polystyrene particles.

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